This invention is directed to a process for providing feedforward control for controlling an amount of elastic material that is fed as part of a larger material handling or converting process.
A number of different manufacturing processes are used to cut continuous webs of elastic material, such as stretch-bonded laminates, into discrete lengths prior to placement in an absorbent garment or other application. Such processes often include feedback control to correct the cut length of the material when cut length errors are detected. The “cut length” is the length of stretch-bonded laminate (SBL), or other elastic material, between consecutive cuts in the machine direction. Feedback control for the cut length of an elastic material typically relies on a cut length error to determine the magnitude of a process correction, with the cut length error being the difference between a measured cut length and a target cut length.
Research has shown that there can be a “stretchability” gradient from the beginning to the end of an SBL roll. For example, if a piece of SBL is cut at the beginning of a roll under a certain tension, and a piece is cut at the end of a roll under that same tension, the cut at the end of the roll may be longer. In a feedback control system, this change in cut length caused by a change in material properties cannot be corrected until an error in cut length has been detected after the panels have been cut. Consequently, sudden changes in material properties or process conditions can result in large errors in cut length because the system is not aware of a change in cut length until after the elastic material is cut.